1. Field of the Invention
This invention relates in general to video recording apparatus, and in particular to apparatus for use in replaying segmented video at various speeds, e.g., fast or slow forward, or fast or slow reverse, or stopped, or at normal record speed, as may be required for the editing of video program material recorded on magnetic tape.
2. Description Relative to the Prior Art
The editing of video program material recorded on magnetic tape is a difficult job. Although there are some video recorders which record discrete fields or frames of video information across the width of a magnetic tape, most video recorders record segmented fields. Quadruplex recorders and many helical recorders fall into this category: A quadruplex recorder lays down 16 widthwise tracks, each track of which corresponds to 16.2 video lines, to record a single video field; a helical recorder such as the BCN recorder, produced by Robert Bosch, GMBH, Fernseh Division, Darmstadt, West Germany, lays down five slantwise tracks, each track of which corresponds to about 50 video lines, to record a video field. Because of the segmenting of the video field information, the recorder tape drive--say for purposes of program editing, etc.--cannot be run at any, or no, speed without employing elaborate, and expensive, buffering equipment, viz. an editing machine. One cannot merely plug, say, the playback signal of a variable tape speed quadruplex recorder into a monitor and get a meaningful display on the monitor, unless the quad tape is replayed at its record speed. Where recorded on quad tape to be stopped, the play heads would repeatedly scan the same 16.2 recorded video lines with attendant tearing apart of the image display; were quad tape to be run, say at high speed, the quadruplex heads would "hopscotch" from segment to segment of different fields, again with attendant tearing apart of the image display.
A current practice in the editing of magnetic tapes is to transfer to and store taped program material, along with frame time/program identifiers, in a random access memory, say as in the CMX Editing System of CBS/Memorex. Such an editing system employs 20 disc recording surfaces, each capable of storing five minutes of skip-field (or 21/2 minutes of full frame) "2 mHz" video information; and monitor apparatus capable of displaying frame and time information. Selectively, editing decisions for splicing tapes, for lap-and-dissolving scenes, etc. are made by viewing the monitor.
Copending U.S. Patent Application Ser. No. 780,945, now U.S. Pat. No. 4,193,098, to Bixby et al discloses a simplified form of machine useful in the editing of recorded segmented video, such machine being so designed as to obviate the need for a relatively large memory. Basically, the editing machine disclosed in U.S. Pat. No. 4,193,098 employs an ancillary recording surface (disc) that is slaved to the rotational rate of the "playback" scanner that cooperates with a primary record medium (tape). The ancillary recording surface has a number of record tracks corresponding to the number of segments which make up any given video field recorded on the primary medium. As the playback scanner swipes along a field segment on the primary record medium, the signal so produced is recorded on the ancillary medium in a respective designated track. As the next field segment on the primary medium is scanned, it too is recorded in a respective designated track. When segments of other fields recorded on the primary medium are scanned, the "segment" signals so produced are recorded directly over corresponding segment signals on the ancillary medium. By assuring that only signals of adequate quality are recorded on the ancillary medium into a monitor display device, the display which is produced will always be coherent, irrespective of whether the playback segments are from the same or different video fields recorded on the primary medium. Because the monitor display is always coherent, it can be used while running the primary medium at other than its record speed (e.g., fast, slow, stopped, reversed) to identify--for purposes of editing--recorded scenes on the primary medium.
In determining whether a played-back segment signal from the primary medium is of sufficient quality to be recorded on the ancillary medium, the apparatus of U.S. Pat. No. 4,193,098 employs "tone codes". That is, each segment of a field has a corresponding tone code signal associated with it. During slewing of the primary medium, say at a speed other than its record speed, the playback scanner will continually cross from one track to another; a "good video" signal will be produced by the playback scanner when the scanner is "on" a segment track . . . which is to say that one tone signal will be detected; between segment tracks on the primary medium, the playback scanner will detect two (or no) tone signals . . . which translates to a "not good video" situation.
Such a technique for determining the quality of a playback video signal has proved to be okay to a point; however, since playback of tone signals is, at least to some extent, dependent on the quality of the primary recording medium, the discrimination between tone signals is, at best, only a coarse indication of signal quality.